1. Field of the Invention
The present invention relates to a choke coil, and more particularly, to a choke coil for use in eliminating noise produced from electronic devices and for preventing noise entering electronic devices.
2. Description of the Related Art
This type of choke coil is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-238636. FIG. 14 is a perspective view of an example of a choke coil. A choke coil 100 includes a magnetic bobbin 112, windings 126 and 128, and a magnetic connecting member 134. The magnetic bobbin 112 has a winding member that has a quadrangular prism shape. End flange portions 116 and 118 are provided at both ends of the winding member, and a center flange portion 120 is provided at the center thereof. The center flange portion 120 has a square shape and is slightly smaller than the end flange portions 116 and 118 (see FIG. 15).
The winding 126 is provided on the winding member between the end flange portion 116 and the center flange portion 120, and the winding 128 is provided on the winding member between the end flange portion 118 and the center flange portion 120. The plate-like magnetic connecting member 134 is placed on the outer peripheral surfaces of the end flange portions 116 and 118 so as to connect the outer peripheral portions thereof. On the other hand, a gap g is formed between the connecting member 134 and the outer peripheral surface of the center flange portion 120, as shown in FIG. 15.
In the above-described conventional choke coil 100, however, when a large normal-mode current is passed therethrough, a magnetic saturation phenomenon occurs, inductance is decreased, and an ability to eliminate normal-mode noise is reduced. In order to solve these problems, conventionally, the magnetic saturation phenomenon is suppressed and the normal-mode noise eliminating ability is maintained by increasing the sizes of the end flange portions 116 and 118 so that the connecting member 134 is spaced away from the center flange portion 120. However, this undesirably increases the height and overall size of the choke coil 100.
In order to overcome the problems described above, preferred embodiments of the present invention provide a low-profile choke coil in which a magnetic saturation phenomenon is minimized.
According to a preferred embodiment of the present invention, a choke coil includes a magnetic bobbin having a winding member, end flange portions disposed at both ends of the winding member, and a center flange-portion disposed at an approximate center of the winding member, a magnetic connecting member connecting the end flange portions at both ends of the winding member, the magnetic connecting member being spaced from the center flange portion by a distance, a first winding wire wound between the end flange portion at one end of the winding member and the center flange portion, and a second winding wire wound between the end flange portion at the other end of the winding member and the center flange portion, wherein at least one of a recessed portion and an inclined portion is provided at an edge of the center flange portion on the side of the connecting member so as to increase the magnetic resistance between the center flange portion and the connecting member.
By providing a recessed portion or an inclined portion at the edge of the center flange portion on the side of the connecting member, the magnetic resistance between the center flange portion and the connecting member is significantly increased. This allows the choke coil to minimize the magnetic saturation even when a large normal-mode noise current is passed therethrough.